1. Field of the Invention
The present invention relates to an image capturing apparatus with a synchronous focusing function, and more particularly, to an image capturing apparatus for focusing a lens synchronously according to a distance between an object and the lens measured by the image capturing apparatus.
2. Description of the Prior Art
Digital cameras have become popular digital products and are positioned to eventually replace conventional film cameras due to low prices and compatibility with other electronic peripherals. There are several shooting modes that can be used according to the distance between an object and a camera lens. When the object is very close to the lens, a user can choose a close-shoot mode (also called macro mode) in which the focus range is be limited within a specific closed-shoot distance so as to shorten the focusing time. If the focusing time is shorter, the accuracy will be increased since there is less chance environmental interruption during the focusing time. For example, please refer to FIG. 1. FIG. 1 is a relationship diagram of the step of a lens driven by a step motor and an object distance parameter. If the object distance parameter is larger, the best object distance is more approximate. When the camera is in the general-shoot mode, the moving range of the lens driven by the step motor is larger than the one in the close-shoot mode. As shown in the FIG. 1, a curve A is the relation curve of the step of the lens driven by the step motor and the object distance parameter in the general-shoot mode, and a curve B is the relation curve of the step of the lens driven by the step motor and the object distance parameter in the close-shoot mode. Compared with the general-shoot mode, the object parameter is more sensitive to the step of the lens driven by the step motor in the close-shoot mode. So in the undulating possible object distance range, the failure possibility due to environmental interruption will be increased. However in the close-shoot mode of the present digital camera, the calculating range of the best object distance is limited within a specific range. Nevertheless, no matter what shooting mode is used, the lens starts to move in steps driven by the step motor from a designated position. That is, the moving steps are all the same in every shoot mode. In the close-shoot mode, a processing module of the digital camera calculates the best object distance within a close-shoot range instead of within the moving step range, but the lens still needs to move using steps just like the other shoot modes.
In the conventional close-shoot mode, the lens of the camera still moves the same distance as in the other modes, so users might fail to shoot due to environmental interruption during the focusing period. Therefore, there is a need to shorten the focusing time in the close-shoot mode so that the shoot quality can be improved.